1. Field of the Invention
The present invention relates to an image display apparatus including electron emitting devices, and a method for forming ribs on a substrate in an image display apparatus.
2. Description of the Related Art
An image display apparatus including electron emitting devices may include a rear plate and a faceplate. The electron emitting devices are formed on the rear plate. On the face plate, light emitting members are formed which emit light when irradiated with electrons emitted from the electron emitting devices. The electron emitting devices are operated in a thin hermetic container (a vacuum container) composed of the rear plate, the face plate, and other members. Hence, the hermetic container needs to have an atmospheric-pressure-resistant structure.
In manufacturing a large-area, thin image display apparatus, in light of weight and cost, spacers for providing resistance to atmospheric pressure are disposed as supports between a rear plate and a face plate.
Japanese Patent Application Laid-Open No. 02-299136 discusses an example employing such spacers. Also, in Japanese Patent Application Laid-Open No. 2000-348651, to prevent a phosphor surface (where light emitting members are provided) of a face plate from being damaged due to, e.g., misalignment or deformation of spacers, ribs are formed on the face plate, projecting from the phosphor surface. In this image display apparatus, the straight ribs of uniform width abut on the spacers. Those ribs prevent the spacers from directly abutting on the phosphor surface of the face plate. Thus, even if the spacers become misaligned or deformed to some degree, the electron emitting devices and the phosphor surface are not damaged, thereby facilitating the assembly of the image display apparatus.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2000-500613 describes a structure in which a scattering shield (ribs) higher than light emitting members by about 20 to 200 μm is provided to reduce the number of backscattered electrons re-entering the light emitting members. Accordingly, ribs not only abut on the spacers that provide resistance to atmospheric pressure, but also function as a scattering shield for reducing the number of backscattered electrons re-entering the phosphors (light emitting members).
In a structure in which spacers abut on ribs formed on a face plate, if the ribs have a uniform height, the load imposed by the spacers can be distributed among all ribs. However, despite efforts to form ribs of desired height, the resultant ribs vary in height to some extent. Consequently, the spacers may abut on ribs of higher height only.
When such ribs of various heights abut on spacers in assembling an image display apparatus, a shear force may be applied to the ribs due to, e.g., misalignment or deformation of the spacers. In that case, the magnitude of the shear force applied also varies among the ribs according to the variations in the height of the ribs. When only a few ribs have higher height, a shear stress produced in those ribs being in abutment on the spacers is increased, which may cause failure of the ribs.
To ensure the strength of the ribs, the ribs may be increased in width. However, the width of the ribs can be increased only to a limited extent because of limitations on the available area where other members, such as light emitting members, are also disposed. If, to overcome these area limitations, ribs of narrower width are formed, rib failure may occur when the spacers abut on those narrow-width ribs.